The present invention relates to an impact dot printing head, and more particularly, to such a printing head of small size.
A known impact dot printing head is shown in FIG. 1. A ring-shaped permanent magnet 1 is assembled in the outer peripheral part of the printing head. A common lower yoke 2 is coupled with one pole side 1-a of the permanent magnet 1. A plurality of iron cores 4 having coils 3 wound therearound; extend upwardly from the lower yoke 2. A common upper yoke 5 is coupled with the other pole side 1-b of the permanent magnet 1. The upper yoke 5 is provided with openings 5-a in its positions opposing the iron cores 4. Armatures 7 fastened to an elastic member (leaf spring) 6 are fitted in the respective openings 5-a in a rockable fashion, with clearances therebetween.
Printing wires 8 . . . are fixed to the fore end parts of the respective members 6. The base end parts of the elastic members 6 are fixed between the upper yoke 5 and a case 9 with screws or the like. In the illustrated state, the armatures 7 are attracted to the respective iron cores 4 against the elastic members 6 by the permanent magnet 1. By energizing the respective coil 3 to generate a magnetic flux in a sense reverse to that of the magnetic flux of the permanent magnet 1, the elastic member 6 is released, and the printing wire 8 is extended through the top portion of by the strain energy stored in the elastic member 6. Thus, the printing operation of the printing head can be carried out.
In the printing head of the above construction in which the printing is effected by releasing respective armature from the permanent magnet, the permanent magnet 1 is arranged outside the iron cores 4 as seen in FIG. 1, and a ferrite type material of low energy product, typically 3-5 mega gauss-oersteds, is principally used for the permanent magnet 1. In order to obtain the energy required for the printing, therefore, the permanent magnet 1 needs a considerable sectional area and height, and its volume occupies a large proportion of the volume of the printing head. The miniaturization of the printing head is accordingly limited.